Processes for the preparation of savoury flavours are known in the art:
GB 1256462 discloses meat-like flavouring compositions and methods of preparing them. The flavouring compositions comprise organic oxygen-containing heterocyclics wherein the second carbon atom from the oxygen atom contains a sulphur substituent.
GB 1434194 describes the preparation of addition compounds from the reaction of mono- or dialkylfurenidones (e.g. 2,5-dimethyl-4-hydroxy-3-(2H)-furanone) with carbonyl compounds, such as ketones. These addition compounds are stable upon storage and, since they are precursors of furenidones, they can be incorporated into foodstuffs where, upon heating of the foodstuffs, they revert to free furenidones, which have flavouring properties.
GB 1283912 and GB 1283913 describe processes for preparing meat-like flavouring substances; the processes comprise reacting certain heterocyclic ketones, such as 4-hydroxy-2,5-dimethyl-2,3-dihydrofuran-3-one or 4-hydroxy-5-methyl-2,3-dihydrofuran-3-one, with hydrogen sulphide or other sulphur-containing compounds (e.g. cysteine) in the presence of water. Although, these processes permit the synthesis of interesting savoury mixtures, they are not very specific, so do not form high yields of key meat flavours (eg. see Examples B1 and B2 of GB 1283912).
EP-A-571031 discloses a process for the preparation of a savoury flavour which comprises reacting mono- and/or di-methyl-3(2H)-furanone, or precursors thereof, with cystein and/or hydrogen sulphide. No hydroxy group is carried in the four position. A suitable precursor is 2,5-dimethyl-2-(2-hydroxy-3-oxo-2-butyl)-3(2H)-furanone, which is a diacetyl oligomer. The process results in high yields of certain key compounds, namely methyl-substituted furanthiols, their disulphides and methyl-substituted furanthiolacetates. The reaction of 2,5-dimethyl-2-(2-hydroxy-3-oxo-2-butyl)-3(2H)-furanone with H.sub.2 S and cystein results in a 32% yield of 2,5-dimethyl-furan-3-thiol (see example 8 of EP 571031 and comparative example D of the present application): FIG. 2 of the present application is a chromatograph of the resultant savoury flavour mixture showing that this key sulphur-containing flavour compound (peak 8) is present.
The present invention seeks to provide a new process for preparing a savoury flavour mixture, the process preferably providing a good yield of a number of key flavour compounds.